This species was described as a small, or pygmy tarsier, based upon three specimens collected in 1917 from central Sulawesi by Henry Raven (Miller and Hollister 1921). Hill (1955) and Niemitz (1984) both treated it as a subspecies of T. tarsier. Niemitz (1985) suggested raising it to full species status. Subsequent analysis by Musser and Dagosto (1987) revealed that two of the original specimens were juveniles of the lowland form (from Gimpu, and therefore, most likely T. lariang), but that another specimen, collected in 1930 from a mountain top in south Sulawesi, was T. pumilus (Musser and Dagosto 1987). The basis for calling this species a "pygmy" form is not strong (indeed, fossil evidence indicates that the ancestral tarsier may well have been small). This species' status as a montane endemic, however, is unequivocal; therefore, we favour the common name "Mountain Tarsier", and perhaps even "Sulawesi Mountain Tarsier", should other forms of montane tarsiers be shown to exist.

Justification:
Listed as Data Deficient since it known only from three specimens, and there is still very little information on its extent of occurrence, status and ecological requirements. We currently know next to nothing of the species; thus, it is recommended that it be reevaluated periodically as more information is gathered and as development pressures change on Sulawesi. Because of the small extent of occurrence (3,700 km2) and the fact that these are severely fragmented populations, the species could possibly qualify for Endangered under criterion B1ab(i,iii,iv,v) if it could be demonstrated that there is a continuing decline due to reduction in extent of occurrence, habitat quality or number of individuals or subpopulations. However, there is currently only localised, small-scale exploitation of the habitat, with limited impact so far. The nature of the montane habitat is such that is remains extremely remote, steep and difficult to access, and so Least Concern is also a plausible listing for this species. What little is known of this species is that it is a small-bodied (approximately 60 g), montane form, endemic to moss forests between 1,800-2,200 m asl. The fact that only three specimens have been found does not presuppose that the species is rare, and if compared to similar small-bodied mammalian taxa, the most likely assumption is that relatively large populations remain. Likewise, comparisons with other nocturnal primates, such as Daubentonia, indicate that such animals can persist relatively unobserved for long periods of time.

This species occurs in southern and central Sulawesi, Indonesia. The first specimen of T. pumilus was collected in 1916 at 1,800 m from Rano Rano, in the mountains between Palu and Poso. The second specimen, collected in 1930, came from 2,200 m on Mount Rantemario in South Sulawesi. A third specimen, which was found dead in a rat trap in May 2000, came from 2,200 m on the flank of Mount Rorekatimbu.

This species has never seen alive by scientists for long time, and is among the least known primates in existence. It has only recently (August 2008) been rediscovered in the wild, captured, radio-collared, photographed, and filmed. Morphological analysis of museum specimens indicates adaptations for life in colder, montane cloud forests (Musser and Dagosto 1987). Moss forests are characteristic of the presumed habitat.

The distribution is in all likelihood fragmented on isolated mountain tops. One threat to these habitats is the encroachment of human populations into montane regions to satisfy the needs of a growing human population. The destruction of montane forests in more densely populated south Sulawesi indicates that this fate may well be in store for Central Sulawesi's montane forests as the human population expands. Some areas of Central Sulawesi near known T. pumilus sites are conflict zones, where factional fighting has seen the dislocation of large human populations that are then resettled in refugee camps. One such site lies along the main route to the Rorekatimbu capture locality.

It is listed on CITES Appendix II. The species is known to occur in at least once protected area (Lore Lindu National Park), although the form likely receives some protection on Mount Rantemario (M. Shekelle pers. comm.).